1. Field of the Invention
The present invention relates to novel thermoplastic, crystalline, organopolysiloxane block copolymers having elastomeric properties, and also to a process for the preparation of such block copolymers by hydrosilylation.
The present invention further relates to certain novel non-elastomeric, crystalline organosilicic copolymers [as well as to the process for their preparation, also by hydrosilylation], which copolymers comprise the rigid blocks of the organopolysiloxane block copolymers.
2. Description of the Prior Art
Amorphous, thermoplastic organopolysiloxane copolymers are known which have elastomeric properties and which are prepared by hydrosilylation of compounds which can easily be purified, by rectification or crystallization, and which bear two SiH groups, with compounds which have the same properties and bear two groups of Si-vinyl type [French Patent Application No. 2,300,779].
These copolymers simultaneously possess the properties of silicone elastomers [excellent resistance to chemical and atmospheric agents] and those of thermoplastic polymers, in particular ease of processing.
However, these non-crystalline copolymers do not withstand high thermal stresses; thus, their modulus of elasticity falls very rapidly at temperatures approaching 100.degree. C. and this prevents their use, for example, in the form of films or membranes in an atmosphere which is maintained in the region of this temperature.
Furthermore, crystalline organopolysiloxane copolymers are known which consist of polytetramethylsilphenylenesiloxane blocks of the formula: ##STR1## and polydimethylsiloxane blocks of the formula --(Si(CH.sub.3).sub.2 O].sub.q', in which formulae the symbols q and q' represent the degree of condensation.
These copolymers can withstand fairly high thermal stresses, their modulus of elasticity falling sharply only at temperatures which are at least in the region of 130.degree. C.
Various processes can be used for their preparation [article by R. L. Merker, M. J. Scott and G. G. Haberland in the Journal of Polymer Science, part A-2, 1964, no. 1, pages 31-44 and article by J. E. Curry and J. D. Byrd in the Journal of APplied Polymer Science, 1965, 9, no. 1, pages 295-311].
However, the process which has been studied most consists, in a first stage, in preparing the polytetramethylsilphenylenesiloxane block by polycondensation, with itself, of the diol of the formula: ##STR2## a polycondensation of this type is not easy to regulate and the desired degree of condensation is not always attained. This block is then condensed with a dimethyl polysiloxane block which is terminated at each end of its chain by a dimethylamino group or a chlorine atom. This condensation generates dimethylamine or hydrogen chloride gas, which should, in principle, be completely removed.
These copolymers are therefore difficult to obtain.